1. Field of the Invention
The invention relates to a chair frame, more particularly to a foldable chair frame of an ergonomic design which can be folded or unfolded both transversely and longitudinally to result in a very compact structure.
2. Description of the Related Art
Referring to FIG. 1, a side leg frame of a conventional foldable chair frame is shown to comprise a first side leg 90 with a front end 95, and a second side leg 91 with a rear end 96. Each of the side legs 90, 91 is provided with a pivot pin hole 93 in an intermediate portion thereof. A pivot pin 94 passes through the pivot pin holes 93 for joining the side legs 90, 91 pivotally to each other such that the latter are foldable and extendable relative to each other. As the front and rear ends 95, 96 are at substantially the same level, the conventional chair frame is not ergonomic. For a chair to be ergonomic, the front end of the chair should be at a position lower than that of the rear end of the chair. In the conventional chair frame, if the level of the front end 95 is lowered, due to the pivotal connection between the side legs 90, 91, the angles between the upper portions and between the lower portions of the side legs 90, 91 are unduly large, which may result in increased loading on the chair frame and damage to the chair frame.
In addition, the conventional foldable chair frame can only be folded lengthwise or sidewise in a single direction and, as such, still occupies a relatively large amount of space.
Therefore, the main object of the present invention is to provide a foldable chair frame of an ergonomic design which can be folded or unfolded both transversely and longitudinally to result in a very compact structure.
Accordingly, a foldable chair frame of this invention includes cross-shaped front and rear leg units, and first and second side frame units. The front leg unit includes a pair of front leg members, each of which has an upper front leg part, a lower front leg part, and an intermediate front leg part between the upper and lower front leg parts. The intermediate front leg parts of the front leg members are connected pivotally to each other. The rear leg unit includes a pair of rear leg members, each of which has an upper rear leg part, a lower rear leg part, and an intermediate rear leg part between the upper and lower rear leg parts. The intermediate rear leg parts of the rear leg members are connected pivotally to each other. The first side frame unit is connected pivotally to the upper front leg part of one of the front leg members, the lower front leg part of the other one of the front leg members, the upper rear leg part of one of the rear leg members, and the lower rear leg part of the other one of the rear leg members. The second side frame unit is connected pivotally to the upper front leg part of the other one of the front leg members, the lower front leg part of said one of the front leg members, the upper rear leg part of the other one of the rear leg members, and the lower rear leg part of said one of the rear leg members. Each of the first and second side frame units includes first, second and third side leg members, and an elongate coupling member. The first side leg member has an upper first leg portion, a lower first leg portion, and an intermediate leg portion between the upper and lower first leg portions. The second side leg member has an upper second leg portion and a lower second leg portion. The third side leg member has an upper third leg portion and a lower third leg portion. The coupling member has a first end section connected to the lower second leg portion of the second side leg member, a second end section connected to the upper third leg portion of the third side leg member, and an intermediate section between the first and second end sections and connected pivotally to the intermediate leg portion of the first side leg member. One of the second and third side leg members is connected pivotally to the coupling member to permit movement of the second and third side leg members away from the first side leg member to an unfolded position. The coupling member is provided with a first limit unit to arrest movement of the second side leg member relative to the first side leg member in the unfolded position, and a second limit unit to arrest movement of the third side leg member relative to the first side leg member in the unfolded position.